This invention concerns an electromagnetic signal horn of a type including a housing, a membrane whose peripheral edge is attached to the housing and which with the housing defines a chamber, an electromagnetic motor arranged in the chamber, and a magnetic core arranged in the chamber with an attaching pin thereof extended through a central opening of the membrane, with a coupling channel thereof, for coupling the chamber with outside atmosphere, being partially defined by a radial recess at the central opening of the membrane.
Such a signal horn is disclosed in german publication 17 66 098. The coupling channel of this known signal horn is partially formed as a radial recess extending from a central opening of the membrane and radial slits in each of two intermediate discs, the discs respectively lying on both sides the membrane.
This known electromagnetic signal horn, however, has disadvantages. That is, when a magnetic core thereof is coupled to the membrane and the intermediate discs are mounted one must be careful that the orientations of the slits of the intermediate discs correspond to the orientation of the radial recess of the central opening of the membrane. This can only be assured, if it can be assured at all, with large fabrication expenditures.
If the above described orientations are not carefully maintained during fabrication, it is possible that the coupling channel will be blocked so that an air exchange between a chamber defined by the membrane in the housing with surrounding atmosphere cannot be assured. In this case, the disadvantages will exist in this prior art device which are particularly intended to be overcome by the device.
German Offenlegungsschrift DE 30 44 555 A1 and U.S. Pat. No. 4,441,099 describe electromagnetic signal horns which likewise have coupling channels for coupling chambers with outside atmosphere. In these known signal horns axially extending grooves are provided in attaching pins for this purpose. These known signal horns are necessarily relatively expensive to manufacture because inclusion of such a groove, or flute, in an attaching pin of the magnetic core requires additional fabrication expense, particularly if the magnetic core is forged as one piece with the attaching pin from one piece of material.
An object of this invention is to provide a signal horn which can be technically manufactured by uncomplicated and cost-effective measures to have a coupling channel for coupling the chamber with surrounding atmosphere, thereby making air exchange between the chamber and surrounding atmosphere possible.